Hypothetical issue A

This is a side thread to> Husbandry as a Whole <<br />
A mind teaser
a thread to make us think what's going on and how to correct.
I have a question and an answer to the question.
I know what's wrong, but want you guys to try to determine what the cause is.
Might be a short thread, but a brain teaser nonetheless :)
Reply as you would to a new-ish TRT member and no idea what
their tank is like or has ever looked like. You know no history of the poster.

Here goes:

Hey TRT, my tank has been running really good
about a year now, and my coral are starting to not look as good over the last
couple of months to the point I thought I better research and try to get some help before things get really bad, or do you think it's just the uglies again?

My params are all good. I'm using RC salt and have a mixed reef tank
mostly zoas and other softies, but a few LPS. I wanted to do some SPS too
but with this recent issue of my coral looking less inflated I wanted to get a handle
on this before I tried anything else.

Any ideas what would cause this deflation or sort of puny looking coral?
Please help!